There are various types of metal forming or forging apparatuses such as a horizontal die casting machine, a vertical die casting machine, a squeeze casting machine, a low-pressure casting machine, a gravity die casting machine, and the like. These apparatuses melt metal in a melting furnace in which the metal is openly exposed to air.
Molten metal rapidly oxidizes upon contact with the air, and this also allows introduction of impurities into the molten metal, thereby forming dross. Although the dross reduces the contact of the molten metal with the air by an insignificant amount, the dross impedes continuous stirring during melting of the metal, thereby reducing the high-quality of the molten metal.